CITS880s Controlled Impedance Test System – tests shorter and fine line traces. See also CITS Assure

Finer geometries and thinner copper can present a challenge for
fabricators measuring impedance on leading edge PCBs. The CITS880s
answers that challenge with the introduction of Launch Point
Extrapolation (LPE). LPE extrapolates the TDR response back to a point
close to the start of the transmission line effectively allowing to
users more accurately to measure the instantaneous or incident
impedance of the line.

CITS880s supports groundless differential test with Polar's unique groundless differential probes which enable on board test where access
to ground points can be a challenge. Groundless differential probes
for the CITS feature a single coaxial connection and are easy to
handle for operators and have lower ownership costs than traditional
differential probes.

The CITS880s is the ninth generation of Impedance test system from Polar
and is a development of the CITS880 which is in widespread use across
the industry. In addition to LPE the CITS880s is able to test shorter
traces – typically 2 to 3 inches shorter than previous generations of
CITS. CITS880s also ships with completely re-engineered IPS high
speed probes which reassuringly are precision molded with ESD
dissipative materials to give maximum protection for your CITS.

Controlled impedance PCBs are used across a broad range of applications to
help ensure high frequency signal integrity. Designers
invariably specify these types of PCBs whenever the edge
speeds of digital signals are faster than 1ns or analog
signals climb above 300MHz.

The characteristic impedance of a PCB trace is determined by the dimensions
of the trace and the properties of the PCB material which can vary from batch to batch. To control trace
impedance PCB manufacturers usually vary trace width to
compensate for different batches of PCB material.
Historically, they were then forced to use specialist
laboratory equipment such as a time domain reflectometer
(TDR) to measure the characteristics of a representative
trace etched on the board or a test coupon. This approach
was complex, expensive and far from ideal in a
production environment.

Many electronics designers – especially those pushing performance
boundaries in the defense/aerospace, communications and
IT industries – are now taking controlled impedance PCBs
a stage further by using differential signals and
balanced traces to improve noise immunity and reduce
timing errors on very high speed interconnects. For PCB
manufacturers serving these rapidly-growing electronics
sectors, verifying the differential impedance of these
balanced traces is now a simple task.

The IPDS probe family is designed especially for use with the CITS880s and combine revised internals with more robust mechanical design and enhancements to the signal path, along with ergonomic precision moldings in 100% ESD dissipative materials. IPS and IPDS probes are easily identified and contrast with previous generation probes by the use of blue labels and blue resist on the probe tip interface.

You can minimize your IPS probe costs to by ensuring your coupons are designed with a "preferred"
footprint please ask your local Polar office for
advice on coupon and testpad geometry.

Groundless differential testing

Groundless probes are available for 2015 editions of the CITS880s and
onwards, both fixed pitch and precision variable pitch groundless probes
are available for situations where OEMs mandate on board test of
differential pairs - and where the ground connection on the PCB is either difficult to access or completely inaccesible.

CITS impedance test systems are
exceptionally easy to use. Powerful Windows-based
software automates every aspect of testing, enabling the
entire process to be controlled by a single click of a
mouse or footswitch. You simply position the IPS probes, select a test file containing the normal PCB test
impedance and tolerance, and press the footswitch. There
is no requirement to perform any of the adjustments that
are conventionally associated with complex TDR
measurements such as setting-up vertical gains, pulse
time delays and timebase values. For maximum throughput,
the CITS can execute a series of impedance tests
automatically, prompting you to reposition the probes as
appropriate.

Test results are simple
to understand – the CITS automatically processes the
data to produce an unambiguous display of characteristic
impedance vs distance, and provides clear visual
indication of pass/fail status. On fine geometry boards which sometimes
exhibit an upward sloping trace, the use of Launch Point Extrapolation
(with the approval of the board design authority) will allow you to better
correlate the impedance test resutls with 2d field solver (such as the
Si8000m) predictions. Use of LPE also makes the measurement
far less subjective to the positioning of the test limits.

Automatic datalogging
enables test results – together with system set-up data
and measurement criteria – to be easily exported to a
wide variety of third-party database or spreadsheet
packages for real-time statistical process control. The
pass/fail status of each test is also made available via
opto-isolated signals on the instrument's rear panel,
facilitating integration with other factory automation
equipment.

All CITS880s now also offer direct export of test results in Excel
compatible format.

Traceable
measurement activity

Traceable
measurement accuracy complements the CITS simplicity of operation. Furthermore, QA
specialists still have the freedom to specify complex
measurement parameters as well as standard test functions
like pass/fail limits, result handling and data logging.

Multi point calibration with reference air lines ensures traceable impedance measurements from under 28 Ohms single ended to over 150 Ohms differential.

You can print test
results to provide conformance reports for your
customers, store the data on disk for archive purposes or
future analysis or export it for real-time SPC purposes.
An optional datalog report generator (DRG) accommodates a wide
variety of standard forms, for simplicity of reporting. A
barcode reader is also available as an option, which
enables PCB identification labels to be scanned-in during
the test process, reducing handling time and eliminating
error.

Design and
process control

When considering starting
impedance controlled production you will also find the Polar Si8000m controlled impedance design system helps you tailor your customers
designs to your production process. It is also ideal in helping your
front end team to optimise the incoming data for maximum controlled
impedance yield. Working with both CITS and Si8000m will give you a
complete solution for impedance test and process control.

Sensitive electronic test equipment like
the Polar Controlled Impedance Test Systems can prove vulnerable to damage
from static electricity if proper anti-static procedures are not followed.
Application Note AP8500 note looks at the best ways to prevent the build up of static charge
in the work area – and avoid expensive repairs to your CITS.